As a kind of new state of matter, Bose-Einstein condensation (BEC) in a dilute gas of trapped atoms is able to exhibit quantum phenomena on macroscopic scales [1]}, [2]}, [3]}, [4]}. Different from pure single-particle behaviour, the interparticle interaction between condensate atoms gives rise to many intriguing nonlinear phenomena. One important example is the dynamics of a condensate trapped in a double-well potential. In this system, the condensate undergoes either Josephson oscillation where the population oscillates sinusoidally between the two wells, or self trapping in which most atoms remain trapped in one of the wells. This has been theoretically predicted [5]} and experimentally demonstrated [6]}, [7]}, [8]}. Recently, in such a double-well model, the quantum phase transition (QPT) and dynamics induced by atom-pair tunneling had also been theoretically investigated [9]}, [10]}.
